1. Field of the Invention
Embodiments are directed to an imaging system, more particularly to an imaging system having relaxed assembly tolerances, and associated methods.
2. Description of Related Art
Image capturing devices have become widely used in portable and non-portable devices such as cameras, mobile phones, webcams and notebooks. These image capturing devices conventionally include an electronic image detector such as a CCD or CMOS sensor, a lens system for projecting an object in a field of view (FOV) onto the detector and electronic circuitry for receiving and storing electronic data provided by the detector.
Conventional imaging system are very sensitive to defocus, as may be seen from FIG. 10, which illustrates a through focus (TF) modulation transfer function (MTF), i.e., MTF versus focus shift in millimeters for light having a wavelength of 0.5461 microns at a spatial frequency of 100 cycles per millimeter for a conventional lens system. The MTF is the spatial frequency response or modulus of the optical transfer function (OTF). The MTF of a system is a measure of the ability of the system to transfer contrast at a particular resolution level from the object to the image, i.e., MTF represents both resolution and contrast. As the spatial frequency increases at the object, it is more difficult for the lens system to efficiently transfer contrast.
FIG. 11 illustrates an exploded view of a digital camera 10. As seen therein, the digital camera 10 may include a lens system 12 to be secured to a lens holder or barrel 14, which, in turn, may be secured to a sensor 16. Finally, the entire assembly may be secured to electronics 18.
When such a digital camera is assembled, the lens system 12 may be screwed into the lens holder 14 until an operator determines that the image is in focus. Due in part to the extreme sensitivity to defocus noted above, assembly of conventional lens systems is very delicate and requires special assembly for each lens in each camera module. The required assembly tolerance is typically a few microns, requiring active alignment. Therefore, there is a need for an imaging system with relaxed tolerances, e.g., that can be made with an assembly process that does not require manual focusing.